Fix several regressions in font selection

In Qt 5.3.0 a change was added which automatically adapts Common
script to surrounding scripts in accordance with the Unicode tr#24.

This broke *a lot* of cases of font selection because the font
selection algorithm is not prepared for handling characters with
adapted scripts. We need to disable this change for now and redo it
later with patches to font selection to avoid the regressions.

[ChangeLog][Text] Fixed several regressions in font selection when
combining different writing systems in the same text.

Task-number: QTBUG-39930
Task-number: QTBUG-39860
Change-Id: Id02b5ae2403c06542ed5d81e7c4deb2e0c7d816e
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/corelib/tools/qunicodetools.cpp

@@ -710,6 +710,7 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
             script = QChar::Script(prop->script);
         }
 
+#if 0 // ### Disabled due to regressions. The font selection algorithm is not prepared for this change.
         if (Q_LIKELY(script != QChar::Script_Common)) {
             // override preceding Common-s
             while (sor > 0 && scripts[sor - 1] == QChar::Script_Common)
@@ -719,13 +720,16 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
             if (sor > 0)
                 script = scripts[sor - 1];
         }
+#endif
 
         while (sor < eor)
             scripts[sor++] = script;
 
         script = prop->script;
     }
     eor = length;
+
+#if 0 // ### Disabled due to regressions. The font selection algorithm is not prepared for this change.
     if (Q_LIKELY(script != QChar::Script_Common)) {
         // override preceding Common-s
         while (sor > 0 && scripts[sor - 1] == QChar::Script_Common)
@@ -735,6 +739,8 @@ Q_CORE_EXPORT void initScripts(const ushort *string, int length, uchar *scripts)
         if (sor > 0)
             script = scripts[sor - 1];
     }
+#endif
+
     while (sor < eor)
         scripts[sor++] = script;
 }

src/gui/text/qtextengine.cpp

@@ -124,7 +124,7 @@ class Itemizer {
         for (int i = start + 1; i < end; ++i) {
             if (m_analysis[i].bidiLevel == m_analysis[start].bidiLevel
                 && m_analysis[i].flags == m_analysis[start].flags
-                && m_analysis[i].script == m_analysis[start].script
+                && (m_analysis[i].script == m_analysis[start].script || m_string[i] == QLatin1Char('.'))
                 && m_analysis[i].flags < QScriptAnalysis::SpaceTabOrObject
                 && i - start < MaxItemLength)
                 continue;

tests/auto/gui/text/qglyphrun/tst_qglyphrun.cpp

@@ -77,6 +77,7 @@ private slots:
     void setRawData();
     void setRawDataAndGetAsVector();
     void boundingRect();
+    void mixedScripts();
 
 private:
     int m_testFontId;
@@ -399,7 +400,7 @@ void tst_QGlyphRun::setRawDataAndGetAsVector()
 void tst_QGlyphRun::drawNonExistentGlyphs()
 {
     QVector<quint32> glyphIndexes;
-    glyphIndexes.append(3);
+    glyphIndexes.append(4);
 
     QVector<QPointF> glyphPositions;
     glyphPositions.append(QPointF(0, 0));
@@ -725,6 +726,23 @@ void tst_QGlyphRun::boundingRect()
     QCOMPARE(glyphs.boundingRect(), boundingRect);
 }
 
+void tst_QGlyphRun::mixedScripts()
+{
+    QString s;
+    s += QChar(0x31); // The character '1'
+    s += QChar(0xbc14); // Hangul character
+
+    QTextLayout layout;
+    layout.setFont(m_testFont);
+    layout.setText(s);
+    layout.beginLayout();
+    layout.createLine();
+    layout.endLayout();
+
+    QList<QGlyphRun> glyphRuns = layout.glyphRuns();
+    QCOMPARE(glyphRuns.size(), 2);
+}
+
 #endif // QT_NO_RAWFONT
 
 QTEST_MAIN(tst_QGlyphRun)

tests/auto/gui/text/qtextscriptengine/tst_qtextscriptengine.cpp

@@ -1258,21 +1258,29 @@ void tst_QTextScriptEngine::thaiWithZWJ()
     QTextLayout layout(s, font);
     QTextEngine *e = layout.engine();
     e->itemize();
-    QCOMPARE(e->layoutData->items.size(), 3);
+    QCOMPARE(e->layoutData->items.size(), 11);
 
     for (int item = 0; item < e->layoutData->items.size(); ++item)
         e->shape(item);
 
-    QCOMPARE(e->layoutData->items[0].num_glyphs, ushort(15)); // Thai: The ZWJ and ZWNJ characters are inherited, so should be part of the thai script
-    QCOMPARE(e->layoutData->items[1].num_glyphs, ushort(1));  // Han: Kanji for tree
-    QCOMPARE(e->layoutData->items[2].num_glyphs, ushort(2));  // Thai: Thai character followed by superscript "a" which is of inherited type
+    QCOMPARE(e->layoutData->items[0].num_glyphs, ushort(7));  // Thai: The ZWJ and ZWNJ characters are inherited, so should be part of the thai script
+    QCOMPARE(e->layoutData->items[1].num_glyphs, ushort(1));  // Common: The smart quotes cannot be handled by thai, so should be a separate item
+    QCOMPARE(e->layoutData->items[2].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[3].num_glyphs, ushort(1));  // Common: Ellipsis
+    QCOMPARE(e->layoutData->items[4].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[5].num_glyphs, ushort(1));  // Common: Smart quote
+    QCOMPARE(e->layoutData->items[6].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[7].num_glyphs, ushort(1));  // Common: \xA0 = non-breaking space. Could be useful to have in thai, but not currently implemented
+    QCOMPARE(e->layoutData->items[8].num_glyphs, ushort(1));  // Thai: Thai character
+    QCOMPARE(e->layoutData->items[9].num_glyphs, ushort(1));  // Japanese: Kanji for tree
+    QCOMPARE(e->layoutData->items[10].num_glyphs, ushort(2)); // Thai: Thai character followed by superscript "a" which is of inherited type
 
     //A quick sanity check - check all the characters are individual clusters
     unsigned short *logClusters = e->layoutData->logClustersPtr;
-    for (int i = 0; i <= 14; i++)
+    for (int i = 0; i < 7; i++)
         QCOMPARE(logClusters[i], ushort(i));
-    QCOMPARE(logClusters[15], ushort(0));
-    QCOMPARE(logClusters[16], ushort(0));
+    for (int i = 0; i < 10; i++)
+        QCOMPARE(logClusters[i+7], ushort(0));
 #ifndef Q_OS_MAC
     // ### Result differs for HarfBuzz-NG
     QCOMPARE(logClusters[17], ushort(1));